1. Operator Overloading

2. Introduction
Mechanism of giving special meaning to an operator is known as operator overloading.
Gives option to give new definitions to operators.
Syntax can’t be changed; but semantics can be.

3. Excluded operators Class member access operators: ( . , .* )
Scope resolution operator ( :: )
Size operator ( sizeof )
Conditional operator ( ?: )

4. Defining operator overloading
To define additional task to operator, define its meaning.
Special function called operator function is used.
General form of operator function is:

5. Operator functions
Operator functions must be either member or friend functions.
Friend Function
Member Function
Unary Operator 1
Binary Operator 2

6. Operator invocation
Overloaded operator functions can be invoked (for unary operator) as:
op x or x op
Can be interpreted as:
operator op (x)
Example: S or S -
Object

7. Operator invocation
Overloaded operator functions can be invoked (for binary operator) as:
x op y
Can be interpreted as:
x . operator op (y)  for member function
operator op (x , y)  for friend function

8. Overloading Unary operators

9. Overloading Unary operators
Using Friend function, it works as:

10. Overloading Binary operators
Consider following example to add 2 complex numbers using friend function as:

12. Overloading + operator

13. + operator overloaded

14. The invocation: C3 = C1 + C2 is equivalent to:
Data members of C1 are accessed directly & that of C2 are accessed using dot operator

16. Overloading Binary operators using Friends
Friend functions can be used instead of member functions for overloading binary operator.
It requires 2 arguments to be passed explicitly; whereas member function requires only one.

17. Previous example can be modified as:
Complex operator + (complex a, complex b) {
complex temp;
temp.x = a.x + b.x;
temp.y = a.y + b.y;
return (temp); }

18. Difference between Friend & Member function
Consider situation where 2 different data types are added as:
A = B + 2;
works for member function, but statement:
A = 2 + B;
will not work.
1st argument used to invoke function

19. Difference between Friend & Member function
However, friend function allows both approaches as:
X op Y
is interpreted as: operator op (X , Y)
And for member function, it can be interpreted as:
X . operator op (Y)

20. Declaration of Operator function
Example
Declaration of Operator function

21. Definition of operator * functions
Example (cont.)
Definition of operator * functions

22. Example (cont.)

23. Point to be noted

24. Type Conversion The statements:
converts x to integer before assigning to m.
Type conversions are automatic for built-in data-types.

25. Consider following statement:
v3 = v1 + v2 //v1, v2, v3 are objects
When objects are of same class, compiler doesn’t complain.
Compiler doesn’t support type conversion for user-defined data-types.
Therefore, conversion routines have to be developed.

26.
Hence, 3 situations arrive:

27. Basic  Class type
Built-in variable (duration) assigned to member variables
Constructor does the job

28. Class  Basic type
C++ allows us to define overloaded casting operator to convert class-type to basic-type.
It converts class-type data to typename.
Example: int num = obj; //object to int

29. Returning “double” value
Example
Returning “double” value

31. One Class  other Class type
Destination Class object
Source Class object
Conversion can be carried out using:
Constructor function
(or)
Conversion function

32. (a) Conversion function (used in source class)
Recall that, Casting operator function:
operator typename()
converts:
class object  typename()
typename() can be built-in or user-defined type.

33. (b) Constructor function (used in destination class)
Here, argument belongs to source class and passed to destination class for conversion.
Hence, conversion constructor is placed in destination class.

34. Example

35. Conversion between objects

36.
Conversion summary